Alternating current-to-direct current (AC-to-DC) converters convert an AC voltage to a DC voltage and can be used in various applications, such as power factor correction (PFC) circuits in televisions and notebooks.
FIG. 1 shows a conventional AC-to-DC converter 100 to convert an AC voltage VIN to a DC voltage VOUT. By way of example, the converter 100 includes a full-bridge rectifier 150, a boost converter 110, and an asymmetrical half-bridge flyback (AFB) converter 120. The boost converter 110 and the AFB converter 120 share the same controller 111. The full-bridge rectifier 150 rectifies the AC voltage VIN to provide a rectified voltage VREC. The boost converter 110 converts the rectified voltage VREC to a DC voltage VLINE. The AFB converter 120 further converts the DC voltage VLINE to a lower DC voltage VOUT. Based on a common control signal, the controller 111 regulates the levels of the voltage VLINE and the voltage VOUT.
If the current of a load powered by the AC-to-DC converter 100 decreases, the power energy consumed by the AFB converter 120 may decrease. However, the boost converter 110 may still transfer the same amount of power to the AFB converter 120. As such, the extra energy which is not consumed by the AFB converter 120 may increase the voltage VLINE, thereby damaging circuit components.